1. Field of the Invention
The present invention relates to a pump device, particularly to a charge pump device.
2. Description of the Related Art
An electronic device normally needs different levels of source voltages. Thus, an electronic device is usually equipped with charge pump devices so as to harness the existing source voltage to generate different levels of source voltages. For example, a flash cell needs different bias voltages in reading, writing (or programming) and erasing. In order to save power, the current electronic devices normally adopt an external source voltage of 3.3V or less. Therefore, charge pump circuits are used to boost voltage so as to supply the required bias voltages of such as 5V, 7V, 9V and 10V to a flash memory.
Refer to FIG. 1. A conventional charge pump device normally comprises a plurality of diodes 10 and a plurality of capacitors 12, whereby to boost or multiply voltage. In such a circuit, two signals having opposite-phase clocks are used to charge or discharge the capacitors 12 so as to boost voltage. If there are N pieces of capacitors 12, the charge pump circuit must spend a time of N periods long for N-fold voltage boosting. In other words, such a circuit takes a pretty long time to boost the voltage to the desire value. Besides, as the conventional charge pump device needs two signals having opposite-phase clocks, the signals thereof should be very accurate lest the circuit be unstable in voltage transition between low level and high level.
Accordingly, the present invention proposes a charge pump device to solve the abovementioned problems.